14th European Conference on Turbomachinery Fluid dynamics & Thermodynamics
Heat Transfer & Cooling
The utilization of design related gaps between assembled turbine components, e.g. purge slots, is a cooling method that is being considered ever more often when dimensioning the coolant air supply protecting the endwall against hot gas. As the nozzle guide vane (NGV) located behind the combustion chamber is exposed to the highest temperatures in the turbine, sufficient cooling is of the utmost importance. Since the turbine components in the real engine experience expansions and contractions within different operational cycles, the aforementioned gaps change in terms of size and geometry. As these gaps can be influenced by design modifications, e.g. slot angle, width and position variations, the dimensioning of the purge air for cooling purposes is the subject of further optimizations. This study investigated the film cooling effectiveness for different configurations of the purge slot in an axisymmetrically contoured endwall NGV, which represents state-of-the-art high-pressure turbine design standards. The current investigation of the film cooling effectiveness is extended from the endwall to the vane fillets, base and surface to evaluate the possible contribution of the purge slot coolant injection to vane cooling. In order to represent changes due to thermal expansion and design modifications, different slot widths, positions and injection angles were examined. In order to quantify the influence of the interaction between main and coolant flow on film cooling effectiveness, different blowing ratios (BR) and density ratios (DR) were investigated. The experiments were performed in a linear cascade equipped with four engine-like turbine vanes at the Institute of Fluid Mechanics and Fluid Machinery of the University of Kaiserslautern. The hot gas path condition was set to obtain a Mach number of 0.75 and a Reynolds number of 225,000 which are typical for modern gas turbines applications. By using flow conditioners, periodic flow was obtained in the region of interest (ROI). The adiabatic film cooling effectiveness was determined by using Pressure Sensitive Paint (PSP) technique. Nitrogen and carbon dioxide were used as tracer gases realizing two density ratios DR = 1.0 and 1.6. The investigation was conducted for a broad range of blowing ratios (0.25 < BR < 1.50). By combining and varying the above mentioned geometric and flow parameters, the measurement campaign included 132 single measurements which provided a contribute to systematic understanding of various parametric effects on cooling efficiency. Therefore, the results will be discussed based on the areal distribution of film cooling effectiveness and its area average.